E-plane probes may be used and operate as an antenna that captures the electromagnetic energy propagating in a waveguide to couple the energy to a microelectronic chip, such as a power amplifier. Typically such E-plane probes are fabricated on separate substrates (alumina and quartz) external to the microelectronic chip.
In power modules according to the prior art, a microelectronic chip, such as a power amplifier, may be connected with a ribbon bond to a microstrip E-plane probe fabricated on a low-loss substrate, which may be alumina or quartz. For such modules, the ribbon bond discontinuity and the microstrip transmission line on the low-loss substrate reduce the performance of the module.
FIG. 1 shows an example of the prior art, showing a W-band GaN power amplifier (PA) WR-10 module, which may have 2 Watts of output power at 94 GHz. As shown in FIG. 1, an E-plane probe 12 extends into a WR-10 waveguide 14. WR-10 may be used for microwave W-band frequencies. The E-plane probe 12 along with an impedance matching circuit 16 is mounted on a low-loss substrate 18. A ribbon bond 22 is used to connect the microstrip transmission line 17 to a W-band GaN power amplifier (PA) 20. The ribbon bond 18 discontinuity and the microstrip transmission line 17 on the low-loss substrate 15 could account for a reduction of over 1 dB in performance.
More recently, and especially for very high frequency operations, such probes have been integrated monolithically on the microelectronic chip.
For example, Donadio, O., Elgaid, K., and Appleby, R. in “Waveguide-to-microstrip transition at G-band using elevated E-plane probe Waveguide-to-microstrip transition at G-band using elevated E-plane probe” Electronics Letters, 47 (2). pp. 115-116. (2011) ISSN 0013-5194 describe a G-band waveguide-to-microstrip transition which is elevated over GaAs substrate; however, the described transition is fabricated with a fabrication process which is not compatible with conventional monolithic microwave integrated circuit (MMIC) processes and requires non-standard micro fabrication steps.
U.S. Pat. No. 6,486,748, issued Nov. 26, 2002 to Stones et al., describes a low-loss transition from microstrip to waveguide using a suspended stripline as an intermediate connection; however, the described transition is fabricated using materials and a fabrication process which again is not compatible with conventional MMIC processes and requires non-standard micro fabrication steps.
K. M. Leong, W. Deal et al. in “A 340-380 GHz Integrated CB-CPW-to-Microstrip Transition for Sub mm-Wave MMIC packaging”, IEEE Microwave and Wireless Component Letters, vol. 19, no. 6, June 2009, pp. 413-415 describe a monolithically integrated E-plane probe for InP substrates. The design described utilizes the entire width of the substrate for the E-plane probe. The disadvantage of such a structure is that because the entire substrate width is used for the E-plane probe, there is a large leakage of the trans-electric TE10 mode in the waveguide into the circuit, which reduces the circuit performance.
K. M. Leong, K. Henning et al. in “WR1.5 Silicon Micromachined Waveguide Components and Active Circuit integration Methodology”, IEEE Trans. on Microwave Theory and Techniques, vol. 60, no. 4, April 2012, pp. 998-1005 describe a monolithically integrated E-plane probe on a InP substrate. The fabrication uses deep reactive ion etching to form the E-plane probe. The approach works with thin substrates; however, does not work with substrate thicknesses greater than 50 um. As a result, deep reactive ion etching cannot create free-standing high aspect ratio structures.
What is needed is an improved way to fabricate E-plane probes for interconnecting high frequency (>100 GHz) microelectronic chips, such as GaN, InP, Si, SiC, GaAs or other technologies with waveguide components. The embodiments of the present disclosure answer these and other needs.